CMOS Image Sensor 1/f Noise Reduction via Transistor Mode Switching
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Solution Overview
Problem
Existing CMOS image sensors face significant challenges in reducing 1/f noise, particularly in source follower transistors, due to pixel size constraints and the complexity of modifying CMOS processes, which affects overall image sensor performance.
Innovation Solution
The solution involves dynamically passivating surface traps in source follower transistors by switching them between accumulation mode and strong inversion mode, reducing 1/f noise through controlled operation of the transistors in CMOS image sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the size of the source follower transistor is increased to reduce 1/f noise, then the 1/f noise is reduced, but the pixel area increases which is not acceptable due to pixel size constraints
Solution Approach 1:
The patent changes the operational parameters of the source follower transistor by switching it between accumulation mode and strong inversion mode. By operating the transistor in accumulation mode during the integration period and switching to strong inversion mode for readout, the patent reduces 1/f noise without increasing the transistor size, thus resolving the contradiction between noise reduction and pixel area constraints
2Object-affected harmful factors
If the CMOS process is modified to reduce 1/f noise, then the 1/f noise is reduced, but the process complexity increases which is not a viable option
Solution Approach 1:
The patent introduces dynamic operation of the source follower transistor, switching between accumulation mode and strong inversion mode at different time periods. This dynamic approach reduces 1/f noise through temporal modulation of transistor characteristics rather than through complex process modifications, resolving the contradiction between noise reduction and process complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces 1/f noise in CMOS image sensors by passivating surface traps, thereby enhancing image sensor performance and noise reduction without increasing transistor size or modifying the CMOS process.
Implementation Method 1
the controller is configured to cause at least one of the transistors in each pixel circuit to be placed in an accumulation mode
Implementation Method 2
switched from the accumulation mode to a strong inversion mode
Implementation Method 3
read noise is typically dominated by the 1/f noise of the source follower transistor. 1/f noise, which is also referred to as flicker noise, has a spectral density that is inversely proportional to frequency (f)
Implementation Method 4
CMOS image sensors sense light by converting incident light (photons) into electronic charge (electrons) via the photoelectric effect
Data Source
AI summary
A CMOS image sensor includes a plurality of pixel circuits. Each pixel circuit includes a plurality of transistors. The image sensor includes a controller for controlling operation of the plurality of pixel circuits, wherein the controller is configured to cause at least one of the transistors in each pixel circuit to be placed in an accumulation mode and then switched from the accumulation mode to a strong inversion mode, thereby reducing 1/f noise of the pixel circuits.